When a single flow turbine is employed in a thermal power system, a thrust load becomes great in one direction. It is therefore required that a balance piston portion having a labyrinth structure should be installed to optimize a load on a thrust bearing.
A single-flow steam turbine of a double casing structure comprising a labyrinth packing to prevent high-pressure and high-temperature steam, which flows into the casing and expands at a blade turbine stage in the casing, from leaking, at a through portion at which a rotor penetrates the casing, has been known. The rotor comprises a rotor blade and a balance piston. An inner casing comprises a stator blade, and forms a high-pressure blade turbine stage together with the rotor blade to surround the rotor. At the through portion at which the rotor penetrates the inner casing, a labyrinth packing is provided between a labyrinth ring of the inner casing and the balance piston.
A recovery pipe for leaking steam which penetrates the labyrinth ring from a middle portion of the labyrinth packing and extends to a steam inlet of a low-pressure blade turbine stage and which has a spout directed to the low-pressure blade turbine stage is provided in a steam chamber between the inner casing and an outer casing. The steam leaking from the labyrinth packing portion is extracted from the middle portion to flow from the spout to the low-pressure blade turbine stage through the recovering pipe and expand.
A steam turbine like the above needs to be equipped with a recovery pipe to recover steam leaking from the labyrinth packing portion. In addition, the recovery pipe needs to be formed of a material resistant to a high temperature since the leaking steam is hot.
Under the circumstances, it is desired to provide a turbine capable of being operated at good efficiency in a simple structure and a method of operating the turbine.